1. Field of the Invention
The present invention relates to the use of acid labile colorants which may be decolorized by acid hydrolysis. In particular, the invention relates to acid labile colorants in the form of polyoxyalkylene substituted azomethine and indophenol chromophores.
2. Prior Art
Fugitive tints which have achieved wide acceptance in the textile industry include the polyethyleneoxy-substituted tints described in Kuhn, U.S. Pat. No. 3,157,633. These tints are normally applied to yarn such as nylon yarn before heat setting. Such tints are a combination of a dyestuff radical and one or more polyethyleneoxy groups. Dyestuff radicals disclosed in the patent above include nitroso, nitro, azo, diphenylmethane, triarylmethane, xanthene, acridine, methine, thiazole, indamine, azine, oxazine, and o-anthraquinone radicals. Preferably, such radicals may be attached to the polymeric constituents of the tint composition by an amino nitrogen.
Fugitive coloration of nylon in particular presents special problems since the tinted yarn, or fabric woven or knitted therefrom, may be subjected to a heat-setting treatment, usually with steam. This heat-setting treatment can at times fix the tint in the fibers so that the yarns remain stained or colored, and the tint cannot be removed readily in later finish-scouring operations. Special and inconvenient reducing or oxidizing treatments to remove the tint may therefore be required.
Also, with the advent of improved continuous carpet dyeing techniques (such as the Kuster Dyer) scouring of the carpet with copious quantities of water is becoming unnecessary and, in fact, may be undesirable, except for the necessity of removing the fugitive tint. These continuous carpet dye ranges are being run at higher speed in order to increase production, further reducing the amount of scouring time that a fugitive tint would experience during dyeing.
Previously, consumers chose darker shades of carpet because they were easier to maintain and did not easily show stains. If the traditional fugitive tint inadvertently left some color on a dark colored carpet, it was often not detectable and did not detract from the appearance of the carpet. With the advent of stain-blocker technologies, consumers are choosing lighter shades of carpet because it is now possible to clean and maintain light colored carpet as easily as dark colored carpet. If any residual fugitive tint is left on light colored carpet, it is more easily noticed and is more likely to detract from the appearance of the carpet.
Furthermore, while conventional fugitive tints have in the past generally been applied at levels below about 0.2% of tint based upon the weight of the fiber, at the present time increasing tint levels are being called for to maintain proper identification of yarn ends during carpet tufting operations. When conventional fugitive tints are used at such higher levels, e.g., above about 0.2%, removal of all of the tint may become increasingly difficult or impossible.